Polyamides are often used in the form of nylon fibers, coatings or molded objects. The usual process for the manufacture of many polyamides involves heating the reactants under reduced pressure so as to remove water of reaction and force the amidation reaction to completion. The molten polymer so produced is then often maintained at elevated temperatures while it is mixed with additives.
Extended exposure to these elevated processing temperatures causes crosslinking of a part of the polyamide. Crosslinks convert the polymer into a gel which is insoluble in molten polymer and in all polymer solvents. Gel collects on the walls of the processing equipment, requiring periodic shut down of the equipment for its removal.
Various techniques have been used for the removal of this gel from the process equipment. The usual industrial method for doing this involves burning of the deposit from isolated equipment parts and mechanical removal but cutting or boring. Various other techniques have been proposed for the removal of polyamide gel without dismantling the equipment. For example, Yamamoto et al. in U.S. Pat. No. 3,669,740 suggested that degraded polymer be contacted at elevated temperatures with a carboxylic acid and optionally an organic hydroxy diluent. In addition, liquids such as the polyhalo alcohols taught by Middleton in U.S. Pat. No. 3,245,944 can be useful in loosening gelled polymer laminated with ungelled polymer, presumably because the latter material is dissolved away.
However, none of these techniques has proved entirely satisfactory, and the burning of deposits from isolated equipment parts and mechanical techniques has remained as the general industrial practice for removing gel.